Proton NMR Studies of Amorphous Plasma-Deposited Films
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Nuclear and Electron Pesonance Spectroscopies Applied to Materials Science
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PROTON NMR STUDIES OF AMORPHOUS PLASMA-DEPOSITED FILMS
JEFFREY A. REIMER and ROBERT W. VAUGHAN Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 JOHN C. KNIGHTS Xerox Palo Alto Research Center, 94304
3333 Coyote Hill Road,
Palo Alto, California
ABSTRACT Proton magnetic resonance data are presented for the hydrogen alloys of plasma-deposited amorphous boron, silicon, carbon, silicon carbide, and silicon nitride. Linewidth and lineshape analysis leads to the conclusion that hydrogen nuclei are clustered in a-Si/C:H, a-C:H, and a-Si/NiH. The a-Si/C:H and a-C:H data show that hydrogen exists in two phases. Modeling of linewidths in a-Si/C:H indicates that the two phases are heavily hydrogenated carbon clusters imbedded in a weakly hydrogenated silicon lattice. Evidence is also presented for the presence of motionally narrowed hydrogen spectra in a-B:H, a-Si/N:H and a-C:H. "B NMR spectra in a-B:H show no evidence of motional narrowing. It is suggested that the hydrogen nuclei giving rise to the motionally narrowed spectra are associated with disorder modes. INTRODUCTION Hydrogenated amorphous thin films have attracted a great deal of attention recently because of their desirable electronic and/or optical properties. Plasma-deposited silicon nitride films have been utilized successfully as passivation layers in high reliability silicon-integrated circuits (1). The remarkable properties of hydrogenated amorphous silicon (a-Si:H) vis-a-vis pure amorphous silicon has lead to the development of p,N and Schottky barrier junctions as well as moderately efficient solar cells (2). The role of hydrogen in these films is not well understood although it is generally accepted that hydrogen passivates dangling bond intrinsic defects and thus decreases the density of states in the gap (2). Recent proton magnetic resonance results have posed some new questions on the role hydrogen plays within plasma-deposited a-Si:H. Lineshape results (3) have shown a-Si:H is characterized by two domains which differ in the local density of hydrogen. Spin-lattice relaxation measurements (4) were recently explained by postulating the existence of hydrogen-containing disorder modes that may contribute to the electronic states in the gap. It is the purpose of this paper to show proton magnetic resonance spectra of amorphous boron (a-B:H), carbon (a-C:H), silicon carbide (a-Si/C:H), silicon nitride (a-Si/N:H). Lineshape and linewidth analysis of these data furnish new information on the spatial homogeneity of these films as well as yield new evidence for hydrogen-containing disorder modes in a-B:H, a-Si/N:H, and a-C:H. EXPERIMENTAL The samples were prepared by an rf-diode deposition system described previous-
348 ly (5) . All samples were deposited onto - 2-inch diameter aluminum foil substrates in thicknesses of -i00l_ resulting in sample masses of 5-100 milligrams after removal of the substrates with dilute
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